West German Patent (DE-PS) No. 10 49 376 describes a method of preparing cyanoalkyl-alkoxysilanes, hereinafter also referred to as cyanosilanes, wherein a chloroalkyl-alkoxysilane is reacted with an alkali metal cyanide in the presence of a solvent at temeratures between 25.degree. and 175.degree. C. under anhydrous conditions. In the practice of the method, after completion of the reaction, the precipitated alkali metal chloride is first separated at room temperature, then the solvent is distilled out, and then the cyanoalkyl-alkoxysilane is distilled out.
This method of operation has the following disadvantages:
The filtering out of the alkali metal chloride must be performed at room temperature so that, after the reaction has taken place, the reaction mixture has to be cooled. When the filtration has ended the filtrate has to be reheated to separate the solvent and cyanosilane, so that this procedure calls for a great expenditure of energy when performed on a technical scale.
Furthermore, the alkali metal chloride can be completely filtered out only in the presence of diatomaceous earth, so that this method requires an additional auxiliary substance.
In addition, the filtering out of the alkali metal chloride requires a great deal of apparatus: Besides the additional filtration apparatus, two more pieces of equipment required, one for the performance of the reaction and one for the distillation of solvents and cyanosilane.